Flow arrangement for multipass heaters



June 2, 1953 J- W. THROCKMORTON FLOW ARRANGEMENT FOR MULTIPASS HEATERS Filed June 16, 1950 ATTORNEY.

Patented June 2, 1953 I FLOW ARRANGEMENT FOR MULTIPASS HEATERS John W. Throckmorton, New York, N. Y., assignor to Petro-Chcm Process Company Inc., New York, N. Y., a' corporation of Delaware I Application June 16, 1950 Serial No. 168,556

6 Claims. (01. 257--255) This invention relates to an improved heating tube arrangement for a single bankof tubes having a multi-pass flow, and more particularly pertains to such an arrangement in which one pass or row of tubes is tipped relative to the other sothat suflicient space is left between the ends of the tubes to connect successive tubes of the same pass by straight-line U bends or straight-line plug type headers, i. e. by bends or headers which are not offset relative to the tubes to which they are connected.

In heaters employing a bank of tubes substantially in one plane and exposed on both sides to the furnace seat, it is a simple matter and no difiiculties have been encountered when the tubes are interconnected at their ends for continuous,

series flow since the usual form of return bends of the U. type are available and suitable for this purpose.

However, it is frequently desirable to interconnect the tubes for multi-pass flow and then the normal return bends cannot be employed because the bends of one pass interfere with the tubes pertaining to the other pass. Special offsetreturn bends or headers have been used to avoid such interference but they introduce other difiiculties since they cause a relatively sudden change in the direction of fiow at the special return bends and thus increase the back pressure in the sysfor a multi-pass bank of heating tubes of less expensive construction than in arrangements heretofore employed.

It is another object to provide a flow arrari'gement for a multi-pass heater in which excessive erosion caused by ofiset headers or return bends is eliminated.

It is a further object to provide a flow arrangement for a multi-pass heater in which the pressure drop of the charging stock is substantially less than in arrangements heretofore employed. T

tubes of each pass are joined at alternate ends by U bends;

Fig.2 is substantially endview of the.=ar-,-

rangement of Fig. 1, but thetubespf each 'pass are joined at alternate. ends by plug-type headers, the latter being shown schematically;

Fig. 3'is a view of the headers of Fig. 2 as seen from line 33;

Fig. 4 illustrates in some detail a plug-type header suitable for use in the arrangement of Fig. 2; and r Fig. 5 is a view corresponding to Fig. 3 of an I arrangement heretofore in common use, in which offset headers are employed.

It is at times desirable to use, in a furnace construction, a single bank of straight tubes with a two-pass flow. In such a bank, the tubes of the first pass alternate with the tubes of the second pass, and the tubes of each pass are joined at alternate ends.

Referring to Figs. 1 and 2 of the drawings, Fig. 1 is a perspective view of a tube arrangement embodying the invention. A first pass 4 comprises a plurality of evenly spaced, straight,

parallel tubes 6, shown as coplanar, having an inlet 8 and an outlet I0. The alternate ends of the tubes 6 are joined by straight-line U bends 12 (that is, they are coplanar with their pass 4) to form a continuous path for fiow of charging stock from the inlet 8, through the tubes ,6 and the bends 12 and thence to the outlet l0.

A second pass l4, similar to the first pass 4, comprises a plurality of evenly-spaced, straight, parallel tubes I6, shown as coplanar, having an inlet l8 and an outlet 20. The alternate ends of the tubes I6 are joined by straight-line U bends 22, to form a continuous path for flow of char ing stock from the inlet 18 through the tubes l 6 and thence to the outlet 20.

The tubes IE or the second bank l4 and the tubes 6 of the first bank 4 are alternately spaced.

The line defined by the midpoints of the tubes [6 of the second pass l4 coincides with the line defined by the midpoints of the tubes 6 of the first pass 4, and the planedefined by the second pass [4 is slightly tipped with respect to the plane defined by the first pass 4, about the above- Fig. 2 substantiallyillustrates in end view the arrangement of Fig. 1, with ajprincipal exception to be noted below. Two straighttubes 24 and 26, I

the latter behind the former, 'represe'nttwo passes 28 and 30, respectively. 'An axis 32 perpendicular 3 points and the tube 26 is rotated slightly about the axis 32.

The only difference between the arrangement of Fig. 2 and that of Fig. 1 is that in the former, the tubes of the passes 28 and 30 are joined at alternate ends by straight-line plug-type headers 34 and 36, respectively, instead of by the U bends l2 and 22 of the latter.

Fig. 3 shows two each of the upper plug-type headers 34 and 36 of the passes 28 and 30, respectively, of Fig. 2, as seen from line 3-3 thereof, but omitting the portions of the tubes 24 and 26 between line 3-3 and the headers 34 and 36. Only one each of the headers 34 and 36'is visible in Fig. 2.

The openings in all the headers: 34 for insertion of the tubes 24 lie in a straight line 38-38; likewise, the openings in all the headers 36 for insertion of the tubes 2E'lie in a straight line 40-40, parallel to and separated in practice by only a few inches from the line 38-38. It is because of this separation that the headers 34 and 3B'may be of the straight-line type.

The headers 34 and 36 appear in Fig. 3 tube slightly bulged outward in-the'ir central portions. This is because the planes of the headers are not perpendicular to line 3 .3, due to the slight-tin ping of the tubes 24 and26 relative to each other.

A conventional straight-line plug-type header 42 suitable for usein the arrangement of Fig. 2 is shown in Fig. 4.- The header 42 comprises a semi-circular tubular body portion 4-4, with anopening 45 in each end 46 thereof for-the inser tion ofparallel heating tubes 48. The entire body portion 44 lies-in the plane defined by the tubes- 48. In line with the openings'45, but-on the outer side of the body portion '44, are two built-up open ports are necessary, such supports would be standard for each tube of each pass.

Many commercial heaters employ tubes which may vary from 20 to 30 feet in-length and it is therefore aparent that the tubes-may make up a bank which is substantially in a single plane even though the tubes are connected in groupswith the tubes of one group-mounted in one-plane which crosses the plane of the other group at a.

very small angle but quite suflicientto enable straight line return bends to be employed at-the ends of the tubes. Figure 2 of the drawings exaggerates the angle which would normally exit between the tube planes.

Fig. is a view similar to Fig. 3, but of an arrangement of the prior art. The'ends of tubes (not shown) of two passes 54 and 55 lieina straight line 5858, necessitating the use of offset headers 60 and 62; Withtheir inherent disa'dvantages noted above, to connect the alternate ends of the tubes of the-passes Hand 55, respectively.

Thus the invention'is well adapted to attaining its objects, and many disadvantages-of the prior art are overcome. The need for the expensive offset headers is obviated, the pressure drop of the charging stock in passing from one tube to the next is greatly reduced, and excessive erosion caused by-ofiset headers or return bends is'elim-' inated.

Obviously many modifications and variations of the invention, as hereinbefore set forth, may be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

Having thus described my invention, I claim:

1. A bank of heating tubes having a multi-pass floW,-cornprising'a first pass including a plurality of straight tubes joined at alternate ends by straight-line return means, a second pass including'aplurality of straight tubes joined at alternate ends by straight-line return means, the tubes of said second pass alternating in said bank with the tubes of said first pass, a centrally located straight line defined by centrally located points of all said tubes, said second pass being tipped with respect to said first pass about said line.

2. A bank-of'heating tubes having a multi-pass flow, comprising a'first pass including a plurality of coplanar straight, parallel tubes joined at al-' ternate ends in series by straight line return means, a second pass including a plurality of coplanar straight, parallel'tubes joined at alternate ends in series by straight-line return means, the

tubes in said second pass alternating in said bank' with=the tubes of said first pass, a straight line defined by the longitudinal midpoints of all said tubes, the-plane defined by'said second pass intersecting the plane defined by said first pass onsaid line.

3. A bank of heating tubes having a multi-pass fiow comprising a first pass and" a second pass, each'said pass including a-plurality of straight, parallel tubes disposed alternately with the tubes of the other pass, the tubes of said first and sec-' ondpasses defining,- respectively, a first plane and a second plane, said first plane intersecting said second plane along a line definedfsubstantially by the longitudinal-midpoints-of all said tubes, saidfirst' plane making 'asmall angle with said second plane, and straight-line return means connecting the tubesof said first and second passes at alter-' nateends.

4: The invention'set' forth in claim 3- whe'rein said straight line return meansare" plug-' type headers.

5. The invention set forth in claim 3 wherein said straight-line-return means-are U- bends.

6. Abanl: of heating'tubes' having multi-passflow, comprising a plurality of'passes, each pass composed of a plurality of coplanar straight paral lel tubes, the adjacent-ends ofwhich are joined by coplanar U shaped passages, the plane ofsaid passages being the-same plane as that of said tubes, the tubes of each-pass being interleaved al- References'Citedin the file-of th is patent UNirED' STATES PATENT 's 

